This invention relates to drive assemblies for eccentrically driven masses having a resilient mounting and, more particularly, to a new and improved drive assembly which avoids degradation of the resilient mounting.
In displacement machines for compressible media which have been proposed as superchargers for engines of passenger automobiles (e.g., "Motortechnische Zeitschrift, 1985, pp. 323-327), the drive assembly is composed of two eccentric devices. The first eccentric device is provided between a centered drive shaft and a driven mass, which in this case consists of a plate formed with spiral displacement ridges on both sides. The second eccentric device is arranged between a secondary shaft, disposed parallel to the drive shaft and driven synchronously therewith, and a bearing boss at the outer periphery of the plate. The drive shaft and the secondary shaft are joined by a toothed drive belt and the eccentricities of the two eccentric drives are the same.
In order to avoid imposing unacceptably high stresses on the moving parts which might occur as a result of manufacturing tolerance build-up or thermal expansion of the eccentrically driven mass, the mounting of the secondary shaft or of the second eccentric device on the secondary shaft or of the driven mass may include a resilient mounting as exemplified by German Offenlegungsschrift No. 31 07 231.
It has been found, however, that the drive shaft is deflected in the region of the driven mass during operation of such a displacement supercharger, which causes an increase in the crank radius by which the drive shaft drives the driven mass. Moreover, the deflection increases as the speed of the drive shaft increases. However, since the eccentricity of the bearing boss with respect to the secondary shaft does not change, a sinusoidal deformation force acts on the driven mass during rotation of the drive shaft, imposing a varying load on the resilient mounting of the guide bearing of the second eccentric device. At high supercharger speeds, a rubber element provided as the resilient mounting is thus acted on by a high-frequency repeated load which may cause destruction of the rubber element.